This result has been a little surprising for scientists – both in the degree the daily cycle can affect radiation levels on the surface of Mars and in the fact that RAD is sensitive enough to track the daily cycle so closely.
REMs has also revealed some surprising aspects of atmospheric behaviour in Gale Crater. Prior to the mission, it had been expected that the large debris mound lying towards and around the centre of the crater (“Mount Sharp”, as NASA calls it, although its correct name is Aeolis Mons) would play a significant role in affecting winds through the crater, giving them a north / south dominance around the rover, which lies slightly north of “Mount Sharp”. REMS has shown this not to be the case, with the winds showing a clear east-west wind dominance, which has caused scientists to think that the crater rim, although much further from the rover than “Mount Sharp”, is having more impact on local atmospheric behaviour than expected.
“With the crater rim slope to the north and Mount Sharp to the south, we may be seeing more of the wind blowing along the depression in between the two slopes, rather than up and down the slope of Mount Sharp,” said Claire Newman, a REMS investigator at Ashima Research in Pasadena, reviewing the data released by the science team in a briefing on November 15th. “If we don’t see a change in wind patterns as Curiosity heads up the slope of Mount Sharp — that would be a surprise.”
It also appears that REMS has recorded evidence of what is now thought to be a common feature on Mars during seasonal changes: whirlwinds, which can in turn give rise to “dust devils.” These have been previously images from orbit and, perhaps most famously, by the MERS rovers Spirit, and Opportunity.
These whirlwinds are thought to have been instrumental in prolonging the operational life of the two MER rovers, both of which use(d) solar panels to generate power for their batteries. The mission team for the two rovers had expected that the efficiency of the solar panels to gather sunlight would decrease over time as dust accumulated over their flat surfaces – which is precisely what happened. However, the MER team were surprised to find the solar panels would suddenly, and seasonally, increase in their efficiency in harnessing sunlight, giving the two rovers regular boosts to their power levels. It is now thought that dust devils “running over” the rovers and “cleaning” the solar panels to be the cause of these seasonal boosts.
Curiosity has yet to see dust devils in Gale Crater, but data returned from REMs contains strong evidence that the rover has actually encountered them. The typical effects of a whirlwind can comprise a combination of the following: a brief dip in air pressure, a change in wind direction, a change in wind speed, a rise in air temperature or a dip in ultraviolet light reaching the rover. REMS has recorded two incidents where all five of these effects were recorded. One possible reason he rover has not physically seen any dust devils directly is that Gale Crater may now have large enough deposits of surface dust which is light enough to be raised by a whirlwind on a sustained basis as it passes.
SAM Gets a Taste of the Action
The past two weeks have seen the soil sampling operations continue with the much-anticipated delivery of the first sample to Curiosity’s suite of instruments collectively referred to as SAM – for Sample Analysis of Mars. The work-up for this has been gradual and has, in part, been the reason why over one-third of Curiosity’s time on Mars has been spent at Rocknest. SAM is the most complex of the science systems aboard the rover, comprising three individual instruments and four subsystems which together allow comprehensive analysis of both air a soil samples gathered on Mars for the presence of organic materials.
As noted in the last mission update in these pages, the three instruments contained with SAM are:
- The Quadrupole Mass Spectrometer (QMS) detects gases sampled from the atmosphere or those released from solid samples by heating.
- The Gas Chromatograph (GC) is used to separate out individual gases from a complex mixture into molecular components. The resulting gas flow will be analyzed in the mass spectrometer with a mass range of 2-535 Daltons.
- The Tunable Laser Spectrometer (TLS) performs precision measurements of oxygen and carbon isotope ratios in carbon dioxide and methane in the atmosphere of Mars in order to distinguish between their geochemical or biological origin.
The four subsystems within SAM comprise:
- The Sample Manipulation system (SMS) for transporting powder delivered from the MSL drill to a SAM inlet and into one of 74 sample cups
- The Chemical Separation and Processing Laboratory, for the enrichment and derivatization of any organic molecules within a sample
- The SAM oven, which heats samples to up to 1000oC in order to release gases for analysis by the science instruments
- The pumps subsystem to purge the separators and analysers.
With regards to the Martian atmospheric sampling, SAM has already seen some use, with two on the three instruments being used to sample the air both at Bradbury Landing and at Rocknest. However, as SAM is also probably the most sensitive of all the systems on the rover, and the mission team have therefore approached using it for soil analysis with a high degree of caution. This has included “cleaning-out” the robot arm-mounted CHIMRA sample pre-processing system with three lots of soil gathered from Rocknest in order to remove any remaining Earth-based contaminants from the interior surfaces of CHIMRA.
Preparations for SAM to receive its first sample of Martian soil commenced with a “practice run” being carried out on Sol 90 (November 6th), when the robot arm was put through an operation to simulate the delivery of a sample of soil to SAM’s inlet port on the top of the rover’s body. This was followed on Sol 92 (November 8th) with the preparation of a sample reception cup within SAM itself, which was then sealed in the sample reception area.
The first delivery of a soil sample to SAM occurred on Sol 93, November 9th, when some 20 grams of Martian surface material was delivery to the waiting sample cup inside SAM from the fifth scoop gathered from the Rocknest sand drift.
A powerful aspect of SAM is the manner in which it can be used for sample analysis. Material deposited within it can be subjected to an initial analysis by the instruments themselves and transmitted back to Earth. Scientists can them examine these initial results and, based on what they see, order SAM to carry out further analysis specifically “customised” to the gathered sample. This is what has happened with the first gathered sample, which was initially analysed remotely by SAM overnight between Sol 93 and Sol 94 prior to the results being transferred to Earth, allowing the science team to determine the additional tests they’d like carried out on the sample. At the time of writing, the results of these further tests have yet to be released.
The First 100 Days and Thanksgiving
Curiosity reached it’s 100th Sol on Mars on November 16th. There was no special event to mark the occasion, and Thanksgiving is likely to pass similarly quietly for the rover. While many in the JPL team will be taking time off from duties, a full set of commands is due to be uploaded to the rover which will include directions for it to complete another comprehensive panoramic imaging of its location and surroundings.
Odyssey Flips Sides
On November 12th, the world’s longest-serving Martian vehicle, NASA’s Mars Odyssey performed a significant step in its operational life. Now eleven years into a remarkable mission, Odyssey switched its primary functions from what is referred to as its “A-side” computer, UHF communications relay and gyroscopic system to its “B-side” systems. Like all of NASA’s vehicles, Odyssey includes a reasonable level of redundancy in its systems to reduce the risk of any single-point failure ending its mission life. This includes its primary computers and system controlling its communications antennae.
Until now, the spacecraft has been using just one set of computer / relay systems – its “A-side” to handle all its functions, including vehicle orientation, communications between itself and Earth (and relaying communications from both Opportunity and Curiosity on the surface of Mars and carrying out its own scientific studies. However, data recently returned to Earth indicated that the A-side’s Inertial Measurement Unit (IMU), which houses the main gyroscope used to control the vehicle’s orientation, was showing signs of wearing out.
The decision was therefore taken to switch operations over to the B-side system before the A-side IMU reached a condition where it may fail. This means that as from November 12th, Odyssey is effectively operating with a new set of computer systems – and the A-side systems can be held in reserve in case something unexpected happens to the B-side systems, which have effectively been “sleeping” for 11 years. Providing no problems occur with the B-side systems (or any other unforseen incident occurs), there is no reason why Odyssey should not still be active in another ten or eleven years.
All images reproduced courtesy of NASA/JPL
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